Things you should already know include how to shuffle, deal, and the basic order of poker play. You should also know what it means to check, call, bet, raise, and fold.
For an introduction to these, and other beginning tips, see www.PlayHomePoker.com
You should also own a set of poker chips of multiple values (or at least multiple colors), a sturdy table, comfortable chairs for all, and a well-lit room. Check out The Tools blogs for more info.